Chem. [mod. f. Gr. ἄνῡδρ-ος waterless (f. ἀν priv. + ὔδωρ water) + -IDE.] A chemical compound formed by the union of oxygen with another element, without hydrogen, but which, on exposure to water, absorbs hydrogen and becomes an acid. Also called anhydrous acids, because they are produced by expelling the water (containing all the hydrogen) from oxy-acids.
1863. Watts, Dict. Chem., I. 295. Very few triatomic anhydrides are yet known. Phosphoric anhydride, P2O5, is the only well known member of this class.
1869. Eng. Mech., 9 April, 58/2. Sulphuric anhydride SO3 when added to water, takes up the oxygen to form a new acid radical.
